Fluid Impregnation of Deformed Preforms

The Resin Transfer Molding (RTM) manufacturing process is frequently used to fabricate parts consisting of doubly curved shells. Woven and stitched bi-directional fabrics deform when draped over tooling surfaces with double curvatures. This deformation results in a corresponding change in the preform's permeability tensor, which will change the fluid impregnation pattern during mold filling stage. This paper presents the results of a study in which flow through deformed preforms was investigated. Experiments were conducted in which two different preforms were radially injected after being sheared to a specified angle. The resulting elliptical flowfronts were used to determine the change in the orientation and degree of anisotropy of the permeability tensor caused by the preform's deformation. The experimental results were then compared with a numerical model developed to describe flow through typical RTM preforms using a deformable unit cell. The anisotropy ratio of the principal permeability tensor was found to increase with the shearing angle as observed experimentally and was verified by the numerical model. The success of the RTM mold design and the accuracy of mold filling simulations are dependent on the use of the correct spatial permeability tensor inside the mold. A predictive model that can provide the permeability changes as a function of local shearing deformation within the draped and compacted preforms should move us closer to a realistic simulation of mold filling in net-shaped composite structures.